This invention relates to lightning rod structures and provides improvements offering a lightning rod a more reliable attraction of high voltage atmospheric electrical discharges giving greater security to its users and the facilities it protects. In order to understand the state of present lightning rod construction technology, the following is a description of how the electrical discharge, which must be attracted towards the lightning rod, is formed in a storm cloud cell.
Experience shows that the phenomenon of the formation of electrical discharges is due to the accumulation of electrically charged drops of water inside a storm cloud cell.
The distribution of the charges inside the cloud cell is not random or unordered, but shown experimentally that the negative charges gather in the lower and central regions of the cloud while all the upper portion is positive. From this it can be said that a storm cloud cell is like an enormous electrostatic charge generator.
A discharge is produced when an electric field is formed in the layer of air between the cloud cell and the ground. The cloud's lower surface and the ground immediately below it behave like the plates of an enormous condenser whose dielectric is the intervening layer of air. The earth's surface is positively charged by induction.
From the lower portion of the cloud, where the negative charge is greater, charges begin to move along a branched tortuous path, sometimes several paths at one time. This process is silent and faintly luminous. As the extremes of these paths approach the earth, they induce a large concentration of positive charges. A highly concentrated electrical discharge occurs from a point on the ground towards the end of the path.
The junction of the ground positive charges and the negative ones from the cloud occurs at a height of 15-50 meters, this discharge being highly luminous and producing thunder. It is at this moment that the current flow is greatest.
Any building protection system must be designed so as to be able to handle this current. Until now, the only protection known and used predominantly has been the "Franklin" type rod or a radio-active one. The principles of both types are in the public domain and together form what can be considered as the state of lightning rod technology.
The construction of radio-active lightning rods came as the result of the necessity for a lightning rod that impeded the formation of atmospheric electrical discharges, something which Franklin type rods could not do. The preventative action of radio-active rods was due to an artifical excitation of the atmosphere producing a greater flow of positive ions than that produced by Franklin type rods. The aim of this flow of ions was to neutralize the electrical charge in the cloud.
However, the construction and installation of radio-active rods has inherent legal and security problems. Precautions must be taken in the handling of radio-active material.